Why are brimondine (alphagan) drops put in the eye before and after argon laser trabeculoplasty procedure?

Prevention. Lasers, including alt and yag capsulotomies, can cause inflammation which can raise the eye pressure. Alphagan (brimonidine) is given to prevent that from happening.
Pressure control. These drops can reduce the risk of a temporary spike in eye pressure following the procedure.

Related Questions

What are brimondine (alphagan) drops used for during a laser trabeculoplasty procedure?

Pressure. They are generally used to lower the pressure in the eye or to help avoid pressure spikes following the laser procedure.